Convergence waveform-shaping circuitry



1968 c. B. NEAL ETAL 3, ,748

CONVERGENCE WAVEFORM-SHAPING CIRCUITRY Filed Dec. 23, 1965 Sheet I of 2 \J l r'-"7'RAc Rzmnce I TRACE Rama:

I T/mc Rsrmc: TRAc Rem/ace G q a TRACE Her/mac INVENTORS CHARLES E NEAL LAWRENCE R. P054 XM 8. M

ATTORNEY Dec. 31, 1968 c. a. NEAL ETAL CONVERGENCE WAVEFORM-SHAPING CIRCUITRY Z of 2 Sheet Filed Dec. 23, 1965 NNR R w H E 0 A LE RR M 353328 w 3 22;; 653 335 2224285; Q23 E3196; 5 w $553 89 A $35 3 555248 N United States Patent 3,419,748 CONVERGENCE WAVEFORM-SHAPING CIRCUITRY Charles B. Neal and Lawrence R. Poel, Batavia, N.Y.,

assignors to Sylvania Electric Products Inc., a corporation of Delaware Filed Dec. 23, 1965, Ser. No. 516,040 9 Claims. (Cl. 315-13) ABSTRACT OF THE DISCLOSURE A gated-type impedance selectively couples at least one convergence coil winding directly and by way of a deflection system to circuit ground to provide an improved waveform shape of current flowing through the convergence coil winding and improved electron beam convergence in the cathode ray tube.

This invention relates to color television receivers and more particularly to an arrangement for converging the electron beams of a multi-beam cathode ray electron device throughout the screen area of the device scanned by the electron beams.

Present-day color television receivers usually include a shadow mask type of cathode ray tube having three guns, a mask, and a screen with triads of phosphor dots aflixed thereto. The three guns provide three electron beams, usually referred to as the green, red, and blue electron beams, which strike the phosphor dot triads and provide the colors green, red, and blue respectively.

A deflection system provides signals which, after proper treatment, and in conjunction with a deflection yoke on the neck of the electron device, cause the electron beams to be deflected in both a horizontal and vertical direction at horizontal and vertical repetition rates. Thus, the electron beams scan the screen of the cathode ray tube in a series of alternating trace and retrace periods.

Although the guns of the cathode ray tube are directed substantially toward the center of the display screen during manufacture of the tube, it can be readily understood that manufacturing tolerances dictate the provision of some means for assuring convergence of the electron beams at the center of the screen area. Further, it is obvious that the convergence of the electron beams at the center of the screen area rapidly deteriorates as the angle of deflection of the electron beams is increased to provide the desired scan of the entire screen. In other words, the fact that the guns are spaced and the electron beams do not pass through the center of a deflection yoke field results in the reproduction on the display screen of individual scan rasters of differing shapes for each electron beam and some means must be provided to converge the differing shapes throughout the entire scan area.

To provide the desired convergence of the electron beams, a convergence yoke having a trio of electromagnets is positioned about the neck portion of the cathode ray tube. Each of the electromagnets includes an adjustable means for effecting static convergence of the electron beams at the center of the screen area of the cathode ray tube.

The convergence yoke also includes horizontal and vertical convergence windings for effecting dynamic convergence of the electron beams during the period of screen scan. More specifically, dynamic convergence of the electron beams is effected by circuit means for providing a flow of current having a substantially parabolic-shaped waveform through the horizontal and vertical convergence windings of the electromagnets. The parabolic-shaped waveform of current is developed such that the current peaks occur during the period of scan retrace and the valley of the waveform occurs at the center of the trace period which coincides with the center of the display screen. Also, means are usually provided for maintaining a substantially uniform magnitude of current flow at the midpoint or center of the trace period to prevent a deleterious effect upon the static convergence of the electron beams by the current flow in the horizontal and vertical convergence windings.

However, with the advent of cathode ray tubes having altered screen curvatures and increased deflection angles, as compared with prior cathode ray tubes, it has been found that convergence of the electron beams throughout the entire scanned area of the display screen of such tubes is most diflicult, if not impossible, with presently known and available apparatus. While presently known apparatus permits convergence of the electron beams in a wide deflection angle cathode ray tube at either the ends of the trace period or intermediate the ends and the center of the trace period, it has not been found possible with known apparatus to obtain convergence of the electron beams at both the ends, the center, and intermediate the ends and the center of the trace period.

Therefore, it is an object of this invention to provide an improved electron beam convergence arrangement for a wide deflection angle multi-beam cathode ray electron device.

Another object of the invention is to provide improved means for shaping a generally parabolic-shaped waveform of current utilized for converging electron beams in a multi-beam cathode ray electron device having a relatively wide deflection angle and employed in a color television receiver.

A further object of the invention is to provide an improved means for controlling the rate of change of current flow with respect to trace period in an electron beam convergence system.

These and other objects are achieved in one aspect of the invention by an arrangement wherein a gated impedance is utilized to shape the waveform of a current flowing through the windings of an electromagnet aflixed to a multi-beam cathode ray electron device having a luminescent screen to provide convergence of the electron beams throughout the entire scanned area of the luminescent screen.

For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the accompanying drawings in which:

FIG. 1 illustrates a prior art voltage waveform commonly applied to the windings of a convergence electromagnet utilized in a color television receiver;

FIG. 2 illustrates a prior art waveform of current flowing in the windings of a convergence electromagnet utilized in a color television receiver;

FIG. 3 is a diagrammatic illustration showing the areas of mis-convergence of the electron beams on the screen of a relatively wide deflection angle multi-beam cathode ray electron device utilizing the voltage and current waveform of FIGS. 1 and 2;

FIG. 4 is a diagrammatic illustration, partly in block and partly in schematic form, of a color television receiver utilizing an improved convergence arrangement;

FIG. 5 is a cross-sectional view of the neck portion of a cathode ray electron device showing the relationship of a convergence yoke thereto;

FIG. 6 illustrates the waveform of voltage with respect to circuit ground developed across a current wave shaping means;

FIG. 7 illustrates the effect of the voltage waveform of FIG. 6 on the voltage waveform of FIG. 1; and

FIG. 8 illustrates the effect of the voltage waveform of FIG. 7 on the waveform of current flowing through the windings of a convergence electromagnet.

Generally, color television receivers employ a cathode ray electron device having multiple guns and a luminescent screen. The guns provide a plurality of electron beams which impinge the screen in a manner such that color rendition is made possible. The electron means are deflected such that they scan the screen area and means are provided for converging the electron beams throughout the screen area scanning. Usually, the color receiver includes a means for providing a potential having a substantially sawtooth-shaped waveform, FIG. 1, wherefrom is developed a current having a substantially parabolicshaped waveform as illustrated in FIG. 2. This current in conjunction with auxiliary apparatus serves to alter the path of the electron beams in a manner such that convergence occurs throughout the scanned area.

As previously mentioned, it has "been found that convergence of the electron beams throughout the scanned area of the luminescent screen of cathode ray electron devices having increased deflection angles and altered screen curvatures is most difficult, if not impossible, with known convergence apparatus. For example, FIG. 3 illustrates the problem encountered in attempts to converge the green and red electron beams in a relatively wide deflection angle electron device with known apparatus. As can readily be seen, green and red electron beam convergence is obtainable at the center and the ends of the scanned area but not intermediate thereto. Further, the green and red electron beams are mis-converged intermediate the center and the left side of the screen and intermediate the center and the right side of the screen. Moreover, it has been found that alterations of known electron beam control apparatus such that convergence of the electron beams is obtained intermediate the ends and the center of the scanned area has a deleterious effect upon convergence at either the ends of the area, the center of the area, or both.

In the embodiment of an improved convergence apparatus, illustrated in FIG. 4, a color television receiver includes the usual converter and IF amplifier stages, video detector and amplifier stages, AFC, chrominance signal synchronizing and demodulating stages, audio stages, and vertical deflection and convergence stages represented by a block 9. Since all of these stages are conventional in this embodiment of the invention, further explanation thereof is deemed unnecessary.

A control voltage available from the automatic frequency control stage, block 9, is applied to a horizontal oscillator 11 to provide synchronization thereof at the horizontal repetition rate. The oscillator 11 provides a synchronized horizontal deflection waveform 13 which is applied to a horizontal deflection system 15. The deflection system 15 develops periodic voltage pulses which, after further treatment, cause the electron beams of a wide deflection angle multi-beam cathode ray electron device 17 to be deflected in a horizontal direction at a horizontal repetition rate. Further, means, to be explained later, are provided for converging the electron beams in a horizontal direction throughout the deflection thereof.

Additionally, means, not shown, are provided for deflecting the electron beams in a vertical direction at a vertical repetition rate. Moreover, means, not shown, are provided for converging the electron beams throughout the vertical deflection thereof.

Referring to the horizontal deflection of the electron beams, the horizontal deflection system 15 includes the cathode ray electron device 17, a transformer 19 having a winding 21, a damper diode 23, a B+ boost capacitor 25, and horizontal deflection windings 27 and 29. The deflection windings 27 and 29 are assembled in a deflection yoke which is disposed about the neck portion 31 of the multi-beam cathode ray electron device 17 having a display screen 33. A periodic flow of current in the winding 21 of the transformer 19 in conjunction with a current provided by the damper diode 23 and B+ boost capacitor 25 flows through the deflection windings 27 and 29 causing the electron beams of the electron device 17 to be deflected in a horizontal direction.

As to convergence of the electron beams of the electron device 17, a convergence yoke, represented generally as 35 of FIG. 4, is positioned about the neck portion 31 of the electron device 17. The convergence yoke 35, illustrated in FIG. 5, includes a first, second, and third electromagnet 39, 41, and 43 representative of the colors green, red, and blue commonly referred to in color television receivers. Each of the electromagnets 39, 41, and 43 includes a horizontal convergence winding 45, 47, and 49; a vertical convergence winding, not shown; and a static convergence means, not shown.

Generally, each of the electromagnets 39, 41, and 43 is associated with an electron beam 51, 53, and 55, often referred to as the green, red, and blue electron beams, and serves to deflect a particular beam in a radial direction with respect to the longitudinal axis of the electron device 17. More specifically, static convergence means, which may be in the form of an adjustable permanent magnet for example, serve to converge the electron beams 51, 53, and 55 at the mid-point of the scan or at the center of the screen 33. Dynamic convergence of the electron beams 51, 53, and 55 is effected by the passage of a current having a substantially parabolic-shaped waveform through the horizontal convergence windings 45, 47, and 49 and vertical convergence windings, not shown. Essentially, the peaks of the current waveform occur at the period of scan retrace while the valley of the substantially parabolicshaped waveform of current occurs at substantially the mid-point of the trace period which is the mid-point of the luminescent screen 35.

As to the development of current flow of an appropriate waveform through the horizontal convergence windings, 45, 47, and 49 of the electromagnets 39, 41, and 43 to provide convergence of the electron beams 51, 53, and 55 throughout the scanned area of a relatively wide deflection angle electron device 17, reference is again made to the embodiment of FIG. 4. Therein, voltage pulses occurring at the horizontal repetition rate in a winding 57 of the transformer 19 in the horizontal deflection system 15 are coupled to a differential type greenred current waveform generating means 59. The greenred current waveform generating means 59 includes a series connected capacitor 61 and variable inductor 63 coupling the winding 57 to a differential inductor 65. A series connected capacitor 67, differential resistor 69, and capacitor 71 are connected across the differential inductor 65 and the alterable arm of the differential resistor 69 is coupled to circuit ground via the adjustable arm 72 of a potentiometer 73.

The differential inductor 65 has a first terminal connected to circuit ground via a current control means 75 including a series connected resistor 77 and rectifier 79 and to a terminal of the horizontal convergence winding 45 of the first or green electromagnet 39. The second terminal of the differential inductor 65 is also connected to circuit ground via the current control means 75 including a series connected resistor 81 and rectifier 83 and to a terminal of the horizontal convergence winding 47 of the second or red electromagnet 41.

A current wave shaping means 85 including a parallel connected resistor 87 and rectifier 89 couples the other terminal of the horizontal convergence winding 45 to a switch 91 which may be directly connected to circuit ground or coupled thereto via a portion 103 of the winding 57. In a similar manner, a current wave shaping means 95 including a parallel connected resistor 97 and rectifier 99 couples the other terminal of the horizontal convergence winding 47 to 'a switch 101 which may be directly connected to circuit ground or coupled thereto via a portion 93 of the winding 57.

Additionally, the winding 57 of the transformer 19 in the horizontal deflection system is coupled to a blue current waveform generating means 105 including a series connected capacitor 107; variable inductor 108; a parallel connected arrangement including inductor 109, capacitor 110, resistor 111; capacitor 112, and alterable resistance 113. The capacitor 112, parallel arrangement, and alter- :able resistance 113 are shunted by a current control means 115 including a series connected resistor 117 and rectifier 119 and by the horizontal convergence winding 49 of the third or blue electromagnet 43.

Generally speaking, the inductors 63, 65, and 108 tend to control the amplitude of the substantially parabolicshaped waveform of current flowing through the horizontal convergence windings 45, 47, and 49 while the resistors 69, 73, and 113 tend to control the tilt or shape of the current waveform. Also, the inductors 63, 65, and 109 tend to have a greater effect upon convergence intermediate the center and the right side of the trace while the resistors 69, 73, and 113 tend to have a greater effect upon convergence intermediate the center and the left side of the trace.

In the operation of the convergence circuitry, the voltage pulses available from the horizontal deflection system 15 are applied to and integrated by the essentially inductive appearing green-red current waveform generating means 59 and would normally provide a potential, as measured from a terminal of the differential inductor 65 to circuit ground, having a substantially sawtooth wave shape as illustrated in FIG. 1. In turn, this substantially saw-tooth wave shape of potential is applied to and integrated by the essentially inductive appearing horizontal convergence windings 45 and 47, respectively, and normally provides a current flow therethrough having a substantially parabolic-shaped waveform as illustrated in FIG. 2.

The current control means 75 serves to clamp the valley of the substantially parabolic-shaped current waveform to a voltage reference level to provide a uniform magnitude of current fiow at the center of the trace period regardless of the amplitude or shape of the current waveform. Thus, the static convergence of the electron beams at the center of the scan remain substantially unaffected by the dynamic convergence currents.

However, in the circuitry of this particular embodiment, as the substantially parabolic-shaped waveform of current, FIG. 2, approaches a minimum at or near the center of the scanning interval, the rectifiers 89 and 99 of the current wave shaping means 85 and 95 respectively change from a conducting to an essentially non-conducting state. Thereupon, the resistors 87 and 97 are essentially connected in series with the windings 45 and 47 respectively. Allowing for the well-known impedance characteristics of the rectifiers 89 and 99 and the slight departure of the waveforms from those obtainable with an ideal switch, the introduction of the resistors 87 and 97 into the circuitry cause an alteration in the rate of change in current flowing through the convergence windings 45 and 47 with respect to the period of trace as illustrated in FIG. 6.

Essentially, the shaping means 85 and 95 respectively serve to alter the waveform of the current flowing through the convergence windings 45 and 47. Further, this current waveform is modified in a direction to improve the convergence at the previously mentioned areas of misconvergence, intermediate the center and the left side of the trace and intermediate the center and the right side of the trace, illustrated in FIG. 3, and, in turn, improve the overall convergence of the electron beams throughout the entire electron beam trace.

In further explanation, reference may be made to potentials readily observable in the circuitry. As illustrated in FIG. 1, a substantially sawtooth-shaped waveform of potential, as measured to circuit ground, normally is available at the junction of the current control means 75 and the convergence windings 45 and 47 respectively. As the saw-tooth shaped waveform of potential advances from a maximum to a minimum value, the rectifiers 89 and 99 changes from the conducting to the essentially non-conducting state causing the resistors 87 and 97 to be essentially connected in series with the convergence windings 45 and 47 respectively.

Thereupon, each of the resistors 87 and 97 have developed thereacross a voltage drop potential having a waveform substantially as illustrated in FIG. 7. Since the voltage drop potentials, FIG. 7, effectively substract from the substantiallly sawtooth-shaped waveform of potentials, FIG. 1, normally available at the junction of the current control means 75 and convergence windings 45 and 47, potentials having a waveform essentially as illustrated in FIG. 8 are provided across the windings 45 and 47 respectively.

Thus, the current wave Shaping means and respectively serve to alter the configuration of the substantially parabolic-shaped waveform of current flowing in the horizontal convergence windings 45 and 47. Further, the alteration in the waveform of current flowing in the windings 45 and 47 is in a direction to provide overall convergence of the electron beams of a relatively wide deflection angle electron device throughout the total area of electron beam scan. Moreover, this current Waveform alteration is in a direction and at a scan location such that the desired convergence intermediate the ends and the center of the trace is effected without a deleterious effect upon convergence obtainable at the ends and at the center of the scan trace.

Additionally, the convergence circuitry relating to the third or blue electromagnet operates in a somewhat similar manner and is well known in the art. Since this particular circuitry is not an essential portion of the present disclosure, further explanation thereof is deemed unnecessary.

It should perhaps be noted that the references to the green, red, and blue colors in the illustrated embodiment are not to be construed as limiting with respect to similar manipulations and convergence of other combinations of colors in a multi-beam cathode ray electron device. Moreover, the above-described manipulations and convergence of the electron beams are not restricted to multibeam cathode ray electron devices of the shadow mask type employing a trio of electron guns in the form of a triad but is equally applicable to shadow mask tubes employing aligned electron guns, tubes having a grid arrangement in the screen area for altering the path of electron flow and numerous other cathode ray electron devices suitable for providing a visual display.

Thus, an arrangement providing improved convergence of the electron beams in a relatively wide deflection angle mnlti-beam cathode ray electron device has been provided. This arrangement not only provides convergence of the electron beams throughout the entire scanned area of the electron device but also accomplishes this desirable feature without deleteriously affecting the convergence of the electron beams at the ends and the center of the scan period.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined by the appended claims.

What is claimed is:

1. In a color television receiver including a multibeam type cathode ray electron device having a viewing screen which luminesces in different colors when impinged by electron beams and a deflection system for directing an alternating trace and retrace of the viewing screen by the electron beams, an arrangement for converging the electron beams comprising:

a plurality of electron beam convergence electromagnets each having convergence coil windings, said electromagnets being in cooperative relationship with the electron device;

current waveform generating means series coupling the electron beam deflection system to each of said convergence coil windings to provide current flow through each of said coils, said current having a substantially parabolic-shaped waveform of alternating peaks and valleys with said peaks occurring substantially at the period of retrace and said valleys Occurring substantially at the mid-point of the periods of trace of the electron beams;

current waveform shaping circuitry including a gatedtype impedance connecting at least one of said convergence coil windings selectively to circuit ground and via said deflection system to circuit ground, said impedance altering the rate of change of current flow with respect to trace period in said convergence coil whereby convergence of the electron beams intermediate the retrace and the mid-point of the trace periods is effected.

2. The electron beam convergence arrangement in accordance With claim 1 wherein a current control means is coupled in circuit with said current wavefonm generating means and each of said convergence coil windings to provide substantially the same magnitude of current in each of said coils at the valley of the substantially parabolic-shaped waveform of current regardless of the shape and amplitude of the waveform.

3. The electron beam convergence arrangement in accordance with claim 1 wherein the gated-type impedance is in the form of a voltage dependent impedance.

4. The electron beam convergence arrangement in accordance with claim 1 wherein each of said convergence coil windings has a pair of terminals and said current waveform generating means provides a potential at one of said terminals causing the development of a substantially parabolic-shaped waveform of current flowing in said winding and said deflection system provides a potential coupled via said current waveform shaping circuit to the other of said terminals causing the development of a substantially sawtooth-shaped waveform of current flowing in said winding.

5. The arrangement in accordance with claim 1 wherein the deflection system includes circuitry providing a signal at a vertical frequency and a signal at a horizontal frequency; each of the electromagnets includes a vertical convergence winding and a horizontal convergence winding; the current waveform generating means includes a means for coupling said vertical frequency signal from said circuitry to said vertical convergence windings to provide a substantially parabolic-shaped wavefonm of current flowing therethrough and means for coupling said horizontal frequency signal from said circuitry to said horizontal convergence windings to provide a substantially parabolic-shaped waveform of current flowing therethrough; and said current waveform shaping circuitry comprises a gated-type impedance coupled in series with at least one of said horizontal convergence windings and said circuitry providing a signal at horizontal frequency.

6. The arrangement in accordance with claim 1 wherein the multi-beam type cathode ray electron device is a threebeam cathode ray tube; the deflection system includes vertical deflection means for providing a signal at the vertical frequency and horizontal deflection means for providing a signal at the horizontal frequency; the convergence electromagnets include a first, second, and third electromagnet each having a vertical convergence winding and a horizontal convergence winding and represent the colors red, green and blue respectively; the current waveform generating means includes vertical current waveform generating means coupling a signal from said vertical deflection means to said vertical convergence winding of said first, second, and third electromagnets to provide a flow of current therethrough having a substantially parabolicshaped waveform and horizontal current waveform generating means coupling a signal from said horizontal deflection means to said horizontal convergence winding of said first, second, and third electromagnets to provide a flow of current therethrough having a substantially parabolic-shaped waveform; the current control means includes a vertical current control means coupled in circuit with said vertical waveform generating means and said vertical deflection winding of said first, second, and third electromagnets to provide substantially the same magnitude of current in each of said vertical convergence windings at the valley of the substantially parabolicshaped current waveform and a horizontal current control means coupled in circuit with said horizontal waveform generating means and said horizontal convergence winding of said first, second, and third electromagnets to provide substantially the same magnitude of current in each of said horizontal convergence windings at the valley of the substantially parabolic-shaped current waveform; and the current waveform shaping circuitry includes a first gated-type impedance connected in series with said horizontal waveform generating means and the horizontal deflection winding of said first electromagnet and a second gated-type impedance connected in series with said horizontal waveform generating means and the horizontal deflection winding of said second electromagnet.

7. In a color television receiver including a multi-beam cathode ray electron device having a viewing screen formed to luminesce in different colors when impinged by electron beams and a deflection system for directing an alternating trace and retrace of the viewing screen by the electron beams, an arrangement for converging the electron beatrns comprising in combination:

electromagnetic means responsive to current flow therethrough to provide a magnetic force for directing the flow path of each of the electron beams, said means being in cooperative relationship with said cathode ray electron device;

waveform generating means coupled to a deflection system for generating a substantially parabolic-shaped waveform of current flow having alternating peaks and valleys with said peaks occurring substantially during the period of retrace of the viewing screen by the electron beams and the valleys occurring substantially at the mid-point of trace of the viewing scren by the electron beams; and

means including a gated-type impedance in series with said waveform generating means and said electromagnetic means for altering the waveform of said substantially parabolic-shaped waveform of current whereby the rate of change of current flowing through said electromagnetic means is materially affected.

8. The arrangement in accordance with claim 7 wherein the electromagnetic means for each electron beam includes a horizontal and a vertical convergence coil winding connected in series intermediate said waveform generating means and circuit ground and the series circuit of at least one of said horizontal convergence coil windings includes a parallel connected resistor and uni-directional conduction device.

9. The arrangement in accordance with claim 7 wherein the electromagnetic means includes a horizontal and vertical convergence coil Winding for each electron beam with a gated-type impedance coupled in series with at least one series connected horizontal convergence coil Winding and Waveform generating means, said deflection system and said remaining horizontal and vertical convergence coil windings being connected in series inter- 9 1 0 mediate said waveform generating means and circuit 3,163,797 12/ 1964 Singleback 31513 grounds. 3,187,218 6/1965 Edel 315-13 References Cited UNITED STATES PATENTS RODNEY D. BENNETT, Primary Examiner. 2 pp 5 F. Assi nt Examiner.

3,114,858 12/1963 Schopp 31513 

